The present invention relates to a hot melt adhesive composition that is useful in laminating together two or more layers in the preparation of a carpet. More particularly, the present invention relates to a hot melt adhesive composition that may be used in the construction of a multi-layered synthetic carpet that provides for 100% recycling of the carpet.
Hot melt adhesives which are heated to substantially softened and preferably molten state, which are then applied to a substrate and allowed to cool and harden are widely used for industrial purposes. For example, such hot melt adhesives have been used in the manufacture of textiles, such as carpets, personal care products, such as diapers and adult incontinence products in the automobile industry such as bonding headliners.
In the area of textiles, and particularly for the manufacture of carpets, it is becoming increasingly important to recycle the carpet trimmings and rejected materials to reduce the amount of waste that presently has to be disposed of in landfills and to improve the manufacturing economics.
Although the utility of the present adhesive composition will be described as it relates to a carpet textile one skilled in the art will understand that the adhesive composition may be used in other applications where recycling of the material is of importance.
Manufacture of tufted pile carpets normally involves tufting a primary backing followed by washing, dying and drying the tufted backing and then subjecting the same to a finishing operation in which a secondary backing is laminated to a backside of the tufted primary backing.
Tufting usually is accomplished by inserting reciprocating needles threaded with yarn into the primary backing to form tufts of yarn. Loopers or hooks, typically working in timed relationship with the needles, are located such that the loopers are positioned just above the needle eye when the needles are at an extreme point in their stroke through the backing fabric. When the needles reach that point, yarn is picked up from the needles by the loopers and held briefly. Loops or tufts of yarn result from passage of the needles back through the primary backing. This process typically is repeated as the loops move away from the loopers due to advancement of the backing through the needling apparatus.
If desired, the loops can be cut to form a cut pile, for example, by using a looper and knife combination in the tufting process to cut the loops. Alternatively, the loops can remain uncut.
Primary backings for tufted pile carpets are typically woven or nonwoven fabrics made of one or more natural or synthetic fibers or yarns, such as jute, wool, polypropylene, polyethylene, polyamides, polyesters, and rayon. Films of synthetic materials, such as polypropylene, polyethylene and ethylene-propylene copolymers also can be used to form the primary backing.
The tufts of yarn inserted in the tufting process are usually held in place by untwisting of the yarn as well as shrinkage of the backing. In the finishing operation, the backside or stitched surface of the backing usually is coated with an adhesive, also commonly referred to as a backcoat, such as a natural or synthetic rubber or resin latex or emulsion or a hot melt adhesive, to enhance locking or anchoring of tufts to the backing. Use of such backcoats also improves dimensional stability of the tufted carpet, resulting in more durable carpets of improved skid and slip resistance.
Generally, the tufted carpet is further stabilized in the finishing operation by laminating a secondary backing, for example a thermoplastic film or a woven or nonwoven fabric made from polypropylene, polyethylene, or ethylene-propylene copolymers or natural fibers such as jute, to the tufted primary backing. The adhesive used in the finishing operation bonds the primary backing to the secondary backing.
In carpet lamination processes, basic requirements for adhesives include ability to bond strongly to the primary backing and bond to the tuft stitches protruding through its backside and the secondary backing. In particular, ability to adhere to nylon and polypropylene is important because the combination of these materials (polypropylene backing fabrics and nylon face yarns) accounts for a large percentage of carpet manufactured at present. Activation temperature of a hot melt adhesive, that is, temperature at which the adhesive softens and flows sufficiently to wet and penetrate the backing surfaces and tuft stitches, must be below the temperature at which the backing and face yarns melt or suffer other damage due to heating, for example, relaxation of oriented polyolefin yarns in the backings. Adhesives also must have a low enough viscosity at temperatures employed in finishing to achieve good wetting of the backings and sufficient encapsulation of tuft stitches to make the tuft yarns resistant to pull-out, pilling and fuzzing. In addition, for commercial practice, economics of a carpet manufacturing process utilizing hot melt adhesive must be at least as good as those of conventional latex lamination techniques which remain the dominant lamination process in commercial carpet manufacture.
A number of hot melt adhesives and processes using the same have been proposed for use in carpet lamination. For example, U.S. Pat. No. 3,583,936 to Stahl discloses a hot melt adhesive having: (1) from about 10-35 weight % ethylene copolymer having about 60-85 weight % ethylene units and about 40-15 weight % lower vinyl ester, acrylate, or methacrylate units; (2) about 10-25 weight % of a wax component having a melting point sufficient to give an adhesive composition with a softening point greater than 190° F.; and (3) about 50-70 weight % of a resin extender that is a blend of (a) an aliphatic thermoplastic hydrocarbon resin that is substantially free of polymerized aromatics prepared from diene and olefin monomers of 5 to 7 carbon atoms and (b) a polymer resin derived from the alkylation of aromatic compounds with dicyclopentadiene and having a softening point of about 40° F.-105° F.
U.S. Pat. No. 3,982,051 to Taft et al. discloses a hot melt adhesive for carpet lamination having consisting essentially of: (1) from about 5% to about 50% by weight of a copolymer of ethylene and unsaturated ester monomer selected from the group consisting of vinyl acetate; alkyl acrylate wherein the alkyl group contains 1-18 carbon atoms; and mixtures thereof; containing from about 40 to 85% by weight of ethylene and from about 15 to about 60% by weight of unsaturated ester monomer; (2) from about 10 to about 85% by weight of an atactic polypropylene; and (3) from about 10 to about 50% of vulcanized rubber, wherein the composition is based upon the combined weight of (1), (2), and (3).
U.S. Pat. No. 3,551,231 to Smedberg discloses a hot melt adhesive carpet lamination process in which molten adhesive consisting of an ethylene-vinyl acetate copolymer and, optionally, waxes (e.g., microcrystalline and polyethylene waxes), fillers (e.g., calcium carbonate), resin extenders (e.g., dicyclopentadiene alkylation polymers) and antioxidant is applied to a tufted primary backing and then a secondary backing is contacted with the so-applied, molten adhesive under pressure after which the assembly is cooled to solidify the adhesive.
U.S. Pat. No. 4,939,036 to Reith discloses a hot melt adhesive composition having about 25 to about 40 weight percent of a polyethylene having a melt index of about 15 to about 30 grams per ten minutes; about 25 to about 40 weight percent of a polyterpene resin having a ring and ball softening point of about 90° C. to about 105° C., about 10 to about 20 weight percent of a paraffin wax having a melting point of about 140° F. to about 165° F., about 10 to about 20 weight percent polybutene having a viscosity of about 500 to about 5000 centistokes at 210° F. and up to about 1 weight percent antioxidant.
Although the aforementioned hot melt adhesives may be used for carpet lamination, it is desired in the textile industry to create products that are 100 percent recyclable with minimum difficulty. Accordingly, there remains a need for a hot melt adhesive carpet lamination process that will provide tufted carpets of good bond strength between primary and secondary backings as well as allow for the carpet to be recycled without physically separating the bonding materials before recycling the carpet material.